1. Field of the Invention
The present invention relates generally to the assembly of electronic devices. More particularly, the present invention relates to the assembly of radio frequency identification (RFID) interposers, inlays, tags and labels.
2. Description of the Related Art
Radio frequency identification (RFID) tags and labels (collectively referred to herein as RFID “devices”) are widely used to associate an object with an identification code. RFID devices generally have a combination of antennas and analog and/or digital electronics, which may include, for example, communications electronics, data memory, and control logic. RFID devices typically further include structures to support and protect the antennas and electronics, and to mount or attach them to objects. For example, RFID tags may be used in conjunction with the security-locks of cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels are described in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,292, the disclosures of which are incorporated herein by reference in their entireties.
As noted above, RFID devices are generally categorized as labels or tags. RFID labels are typically substantially planar RFID devices that are adhesively or otherwise attached directly to objects. RFID tags, in contrast, are secured to objects by other means, for example, by use of a plastic fasteners, a band, or by other fastening means.
In many applications, the size and shape (i.e., the form factor) of RFID devices, and their mechanical properties, such as flexibility, are critical. For reasons such as security, aesthetics, and manufacturing efficiency, there is a strong tendency toward smaller form factors. Where thinness and flexibility are desired, it is important to avoid materials (such as bulky electronics) and constructions that add undue thickness or stiffness to the RFID tag or label. On the other hand, RFID devices must have robust electrical connections, mechanical support, and appropriate positioning of the components (i.e., the chips, chip connectors, antennas) to withstand, e.g., the rigors of shipping and handling. Structures for these purposes can add complexity, thickness and inflexibility to an RFID device.
Another significant form factor, for example, in thin flat tags and labels, is the area of the device, and the performance requirements of the antenna can affect this factor significantly. For example, in the case of a dipole antenna, the antenna typically should have a physical length approximately one-half wavelength of the RF device's operating frequency.
RFID tags and labels typically include an integrated circuit microchip (“chip”) electrically coupled to an antenna. Typically, the antennas are provided on a continuous sheet or web, and the RFID circuit is precisely placed onto a particular antenna using commercially available pick-and-place machines. These machines are relatively slow, and usually require an intermittent indexing process whereby the antenna web stops for a short period of time while the chip is placed onto an antenna on the antenna web. Since the spacing of antennas on the antenna web can be relatively large, for example, 5 to 8 cm (2 to 3 inches) apart, the speed of the production process is further reduced because the antenna web must move a relatively large distance for the next placement operation to take place. Pick and place equipment generally has the highest placement rate when the chip placement locations are very close together.
In many applications it is desirable to reduce the size of the electronics as much as possible. In order to interconnect very small chips with antennas in RFID inlays, it is known to use an intermediate interconnective or coupling structure, variously called an “interposer”, “strap”, and “carrier”, to facilitate device manufacture. Interposers include conductive leads or pads that are electrically coupled to the input/output (“I/O”) contact pads of the chips for coupling to the antennas. These pads may be used to provide a larger effective electrical contact area than a chip precisely aligned for direct placement without an interposer. The larger coupling area provided by the interposer effectively reduces the accuracy required for the placement of a chip during manufacture while still providing an effective electrical connection between the chip and an antenna. Chip placement and mounting are serious limitations for high-speed manufacture. The prior art discloses a variety of RFID strap or interposer structures, typically using a flexible substrate that carries the strap's contact pads or leads. RFID devices incorporating straps or interposers are disclosed, for example, in U.S. Pat. No. 6,606,247 and in European Patent Publication 1 039 543, both of which are incorporated by reference herein in their entireties.
One method for forming an RFID device is described in International Application Serial No. PCT/US03/01513 filed on 17 Jan. 2003. In PCT/US03/01513 chips or interposers are singulated from a first web and transferred to antennas on a second web. The pitch of the chips or interposers on the first web is generally smaller than the pitch of the antennas on the second web. The chips or interposers are generally singulated and transferred to the second web by a continuously moving transfer member that picks and places the chips or straps onto the antennas on the second web. The chips or straps are indexed to the antennas by the transfer member.
Another method of placing an RFID circuit onto an electrical component is described in U.S. patent application Ser. No. 10/947,010 filed on 22 Sep. 2004. In Ser. No. 10/947,010, a transfer drum transfers chips or interposers to a moving web of electrical components by picking a chip when the transfer drum is stationary, and transferring the chip to the moving web when the transfer drum is rotating such that a tangential velocity of the transfer drum is substantially equal to the linear velocity of the moving web. By varying the rate of rotation of the transfer drum, the transfer drum can pick a chip while stationary and place the chip onto an electrical component on the moving web thereby indexing the chip to the electrical component.
Although the use of straps or interposers involves an extra step in the process of attaching an RFID circuit to an antenna, straps or interposers offer an advantage in speed of transfer to the web of antenna structures. A second advantage to the interposer is a reduced requirement for placement accuracy onto the antenna. The respective contact pads of the interposer and antenna can be much larger than those required for the RFID circuit to antenna connection, thereby enabling the use of interposer placement equipment operating at higher speeds and with lower precision requirements.
Interposers offer the advantage that they may be attached to an antenna on a moving web. However, the web speed and production rate are still quite low. Some of the difficulty arises from the difference in spacing of the straps or interposers on the carrier web, and the spacing of the antenna structures to which the interposers will be attached. PCT Application WO 2004/088571 A2, for example, describes a process and apparatus for attaching RFID “modules”, i.e., interposer assemblies, to antennas on a moving web.
One method of assembling interposers begins with a web of interposer leads or pads and a web of RFID chips. Typically the RFID chips are separated from the web and placed onto the interposer leads using pick-place techniques. The chip may be placed onto the interposer leads with a rotary pick-place device for picking RFID chips and placing the chips on interposer leads on a web, thereby forming an interposer assembly. Alternatively, a web of chips may be laminated directly to a web of interposer leads.
As used in the specification and claims of the present patent application, the term “RFID circuit” encompasses both an interposer, and an RFID chip electrically coupled to the interposer.
Often the “pitch” of the RFID circuits on a first web, also referred to as the center-to-center distance between adjacent elements, may be different than the pitch of the interposer leads or other electrical components on a second web. The pitch of chips may be different than the pitch of an array of RFID tags or labels to be formed: (a) in the longitudinal (also called the “down web”) direction; (b) in the transverse (or “cross web”) direction, or (c) in both directions. The difference in pitch may be due to, for example, the size of the elements themselves, manufacturing considerations, and/or efficiency considerations. In general, it is preferable from an efficiency standpoint to have the smallest pitch possible between chips on the first web. Due to the relatively small size of the chips or strap compared to antenna or other electrical elements, the chips or straps are relatively much more closely spaced together. Thus, when placing RFID circuits from a web having a first pitch to an antenna on a web having a second pitch, the chips must be indexed to the antennas, or vice versa. In the interest of efficiency, the indexing process should be performed as seamlessly as possible, preferably without interfering with the advance of the web containing antenna structures.
Therefore, a high-speed method and device is provided for singulating or separating interposers from a first web having a first pitch and transferring the interposers to a transfer device whereby the interposers can be indexed and placed onto electrical components on a second web having a second pitch.